Throughout the world, as a part of the Integrated Pest Management (IPM), botanicals are evaluated for its efficacy against the polyphagous Pink Bollworm Helicoverpa armigera armigera Hubner. In our present study, hexane extract of the dry leaves of the milky mangrove tree Excoecaria agallocha L. exhibited dose-dependent growth inhibition of late 2nd & early 3rd instars larvae of H. armigera under in vitro conditions. 0.1% of crude hexane extract of E. agallocha leaf caused 50% mortality of early 3rd instars larvae of H.armigera (LC50-0.0001g/kg body weight), compared to synthetic pesticide Ekalux (90%)& the solvent control (12%). 2% extract dosage reduced the healthy adult moth emergence to 2% extract dosage ruduced the healthy adult moth emergence to 2% compared to Neem control (14%). Out of the 7 column fractions (SiO2 60-120 mesh, Eluent: Petroleum Ether: Ethyl Acetate) tested, fractions 1,4 & 5 suggested growth inhibition (75%, 151.7 mg), while taraxerol exhibited 80% larval mortality (Mean larvae weight: 64 mg), compared to the controls (416.5 mg on average). Transverse Sections (T.S.) of the midgut of H. armigera larvae treated with the bioactive fractions suggested drastic shrinkage & lysis of the gut wall, leakage of exocrine secretions & the micronuclei. Further studies would suggest the possibility of formulating a pote4ntial phytochemical pesticide from E.agallocha against lepidopteron pests.